1. Field of the Invention
The invention relates to a pneumatic percussion tool comprising a cylinder, a socket for a working tool and a piston arranged displaceable in said cylinder and acting as an oscillating striking member, said piston being provided with a first surface to be acted upon by compressed air for propelling said piston in forward direction towards said working tool, a second surface, facing away from said first surface, to be acted upon by compressed air for propelling said piston backward, and with two striking surfaces, by which a strike on said tool can be effected at both dead centers of said piston oscillations, each to generate a pulse advancing said working tool into a workpiece or retracting and loosening said working tool from said workpiece, respectively, said percussion tool comprising at least one transfer port between said first and said second surface, said port being controlled by said piston, and at least one air outlet, said port and said outlet controlling the compressed air distribution for the piston forward and backward movement.
2. Description of the Prior Art
A penumatic oscillating tool or percussion tool, respectively, for bone preparing tools, especially for rasps for the working of the bearing surfaces of bones that shall receive an artificial joint member, is is known from the Swiss Patent No. 661 239 (corresponding to U.S. Pat. No. 4,651,833). It has been found, however, that despite the loosening action exerted on the working port of the tool, an optimum action of such a tool is not attained, since the rearward momentum is too low to securely retract the tool from the cavity.